LeetCode852. 山脉数组的峰顶索引

题目传送门：852题

class Solution {
public:
    int peakIndexInMountainArray(vector& arr) {
        int l = 0, r = arr.size() - 1;
        while (l < r) {
            int mid = l + r + 1 >> 1;
            if (arr[mid] > arr[mid - 1]) l = mid;
            else r = mid - 1;
        }
        return r;
    }
};